The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
As mentioned above, the invention is particularly applicable to an unmanned aerial vehicle (UAV). Accordingly, the invention will primarily be discussed in relation to that application. However, it should be understood that the invention may have application to various other vehicles, machines, apparatus and devices having internal combustion engines which require fuel and lubrication.
Operation of a UAV on missions likely to encounter high altitude conditions or likely to involve prolonged operation in cold environments can present challenges in relation to oil lubrication requirements for an internal combustion engine powering the UAV. This can be particularly so in circumstances where extremely low ambient air temperatures are experienced (say, for example, temperatures in the order of 30° C. below freezing). In such low temperature conditions, it can be difficult to adequately and reliably pump lubrication oil, which is likely to have a very high viscosity owing to the extremely low temperature, in sufficient quantities to satisfy the lubrication requirements of the engine.
Accordingly, there is a need to heat (warm) the lubrication oil to facilitate pumping of the oil in an effective and robust manner.
For this purpose, it may be advantageous to provide an unmanned aerial vehicle (UAV) with the capacity to heat (warm) lubrication oil for the UAV engine relatively rapidly using heat sources onboard the UAV.
In the design of a UAV, the position of the centre of gravity and moments of inertia can also be very important in relation to the stability and performance of the UAV in flight. In this regard, an important consideration is the configuration and layout of the engine system for propulsion of the UAV, particularly for a UAV having an engine system incorporating an internal combustion engine.
Distribution of mass within a UAV is very important, and mass of onboard fuel contributes to the total mass of the UAV. Fuel consumption throughout a flight leads to progressive changes in the mass of the onboard fuel and so affects the total mass of the UAV. In view of this, it is common design practice to locate a fuel tank at or close to the centre of gravity such that any variation in the fuel mass does not cause a significant shift in the position of the centre of gravity and hence affect moments of inertia for the UAV.
In the design of a UAV, regard must also be had to lubrication requirements of a UAV internal combustion engine. With certain fuelling systems for two-stroke internal combustion engines, the lubrication oil is supplied with the fuel, the lubrication oil being mixed with the fuel to provide what is known as a “pre-mix”. With this arrangement, the fuel tank is filled with the pre-mixed oil and fuel, and accordingly there is only one liquid volume (being the pre-mix within the fuel tank) that needs to be accounted for in the design process.
However, not all fuelling systems can operate effectively using pre-mixed oil and fuel, and in certain cases it is common to deliver lubrication oil to the engine separately of the fuel. This is typically done by way of an engine lubrication system comprising an oil tank and an oil pump for delivering oil from the oil tank to the engine. While this can be effective in satisfying lubrication requirements for the engine, it does introduce additional mass factors into UAV design considerations, and in particular it introduces another liquid volume (being oil within the oil tank) that needs to be accounted for in the design. As with fuel, the lubrication oil is typically consumed during flight and so regard must be had to the progressively varying mass within the oil tank.
A UAV may need to accommodate not only the engine system, but also avionics and often payloads. Where there are size constraints for a UAV, there can be challenges in accommodating these various requirements, particularly in a configuration and layout which is required to satisfy design considerations with respect to the centre of gravity and moments of inertia for the UAV.
Accordingly, it may be advantageous for there to be some integration of the fuel system and the oil lubrication system to provide a compact arrangement which assists is satisfying design considerations.
It is against this background that the present invention has been developed.